Size distribution of trace elements and polycyclic aromatic hydrocarbons in fly ashes generated in Greek lignite-fired power plants

The fly ashes arrested by the electrostatic precipitators of four large lignite-fired Greek power stations (total installed capacity 4048 MW) were investigated regarding the distribution of 27 major, minor and trace elements and 13 polycyclic aromatic hydrocarbons (PAHs) in six size ranges from <40 to >105 μm. An inverse relationship of concentration with particle size was observed for trace elements, such as As, Se, Zn, Pb, Cd, as well as for Ca, whereas the distribution of the matrix elements Al, Si, Ti, Fe, Mg was fairly flat up to 105 μm with relative enrichment or depletion in larger particle sizes. A reverse relationship of concentration with particle size was also revealed for all PAHs, particularly the heavier compounds. The percent mass of all elements and PAH species in the suspendable fraction (<63 μm) was between 25 and 30%. In all fly ashes, the PAH mixture was dominated by 4-ring species (48–62%) followed by 3-ring compounds (38–41%), whereas the carcinogenic 5- and 6-ring PAHs were less abundant (2–11%). Fly ash PAH concentrations were found to correlate strongly with the concentrations of certain trace elements either positively (e.g. Ba) or negatively (Mg, Cr, V, U) thus suggesting that some lignite elements might promote or prevent PAH formation during combustion. The suspendable fly ash fraction (<63 μm) was found to contain 6–35% of the total mass of individual elements and 10–57% of the total mass of individual PAH components.